Re: draft-shand-remote-lfa-00 / RFC 5286 / draft-ietf-rtgwg-lfa-applicability => using low BW link as LFA to protect high BW link

    Hi Stephane,
    if link which you want to exclude is local to the calculating router 
then implementation is trivial and doesn't need any signaling.
    If link is not local then this is very similar to more general 
problem of non-local SRLG. It was discussed but computation is 
relatively complex and still needs investigation.

Anton

On 01/17/2012 05:35 PM, stephane.litkowski <at> orange.com wrote:
> Hi all,
> I made some simulation based on real topologies on LFA and remote LFA.
> I saw some issues related to topologies and I wanted to have some
> feedback on it.
> We focus on P-P link failures.
> In some ring topologies between Ps (which doesn't work very well with
> LFA), alternate Ps are not eligible for LFAs (for some destinations) but
> some PEs are eligible providing link protection for the P-P link failure.
> We tried to apply remote LFA algorithm for non LFA eligible
> destinations, and sometimes we have the same thing : PEs are used as
> best rLFA because there is no eligible P.
> PE are sometimes meshed with low BW link (compared to core links). So if
> P core link fails, traffic will be switched on PE link (during
> protection time) and so will potentially (high probability) make the
> link congestionned.
>  From P point of view : traffic is protected, even if some traffic is
> dropped due to congestion(CoS should prioritize traffic), it's better
> than dropping all.
>  From PE point of view : some destinations of the PE where maybe not
> using the P-P link that fails. But due to congestion of the link, they
> become impacted. So impact for the PE is maybe greater than not having
> LFA on the core (we are talking about few seconds of impact -> time for
> the P to converge).
> Note : it's not a one to one mapping of traffic between the P-P link
> that fails and the P-PE link used as LFA. It will depend on how many
> destinations are using this PE as LFA (and quantity of traffic per
> destination). But we could clearly expect congestion as PE links are
> sized only for their usage.
> Do you think this is a real concern ?
> If yes, is there already a proposal/solution to deal this issue ?
> - like using TE informations (ISIS subTLV) to take account BW, and so
> basically not protecting a link by a lower BW link
> - preventing some links to be used as LFA
> Thanks for your feedback
> ---
> Stephane
>
> _________________________________________________________________________________________________________________________
>
> Ce message et ses pieces jointes peuvent contenir des informations confidentielles ou privilegiees et
ne doivent donc
> pas etre diffuses, exploites ou copies sans autorisation. Si vous avez recu ce message par erreur,
veuillez le signaler
> a l'expediteur et le detruire ainsi que les pieces jointes. Les messages electroniques etant
susceptibles d'alteration,
> France Telecom - Orange decline toute responsabilite si ce message a ete altere, deforme ou falsifie. Merci
>
> This message and its attachments may contain confidential or privileged information that may be
protected by law;
> they should not be distributed, used or copied without authorization.
> If you have received this email in error, please notify the sender and delete this message and its attachments.
> As emails may be altered, France Telecom - Orange shall not be liable if this message was modified, changed
or falsified.
> Thank you.
>
>
>
> _______________________________________________
> rtgwg mailing list
> rtgwg <at> ietf.org
> https://www.ietf.org/mailman/listinfo/rtgwg